1. Field of the Invention
The present invention pertains to systems which support and insulate elongated electrical conductors and more particularly, to an apparatus for insulating high current electrical bus conductors by clamping the bus conductors with insulating clamping members suspended within a bus duct.
2. Description of the Related Art
Electrical power distribution networks and switchgear systems require that high voltage electrical bus conductors be electrically isolated from other conductors and environmentally protected from indoor contaminants and from outdoor elements in order to safely deliver power to various points in an electrical system. Of interest here are support structures which insulate electrical bus conductors within ducted chambers, by insulatively supporting the electrical conductors. Examples of some applications with these requirements include mass transit systems, power distribution networks, power generation systems and various industrial applications.
Electrical bus conductors may have either a circular or an elongated cross-section. Attention here will be drawn to the latter configuration, commonly termed "bus bars." Bus bars are available in a variety of sizes, so it would be desirable to accommodate a variety of such conductors with a limited number and type of insulation and support parts. A "one size fits all" solution is desirable because significant savings in production and inventory costs may be realized. Also, labor costs are reduced, because systems are more easily and quickly assembled. Moreover, damaged parts of an assembly may be readily replaced by standard stock components.
There are two types of insulating support structures currently in use today. They include through-type insulators and standoff insulators.
A through-type insulator slides onto a bus bar. The insulator is then supported within the bus duct by being attached to an internal framework using bolts or other fasteners. Basically, these insulators are one-piece parts with a slot or hole in the center for receiving the bus bar. The slot is dimensioned to fit a specific bus bar size.
Alternatively, bus bars may be supported on standoff insulators, typically made of porcelain or other ceramic. Although the standoffs insulators may be used with many bus bar sizes, this is accomplished by drilling holes into the bus bars to bolt them to the standoff insulators. Since drilling holes through a bus bar compromises its insulating jacket and creates the potential for corona arcing, the bus bar must be re-insulated before being used. The holes also increase the electrical resistance of the bus bar. Moreover, the operation of drilling holes and attaching standoff insulators is labor intensive.
It would also be desirable for bus bar support members to be adjustable, allowing the intervals between bus supports to be shortened or lengthened as needs change. An adjustable bus support structure provides a flexibility which may ultimately lead to cost reduction through labor savings, by eliminating a need for design work, and by providing an ability to upgrade the application without major modifications. The through-type bus support insulator can be relocated, but only with a great deal of difficulty, requiring new holes to be drilled in the support duct in which they are enclosed, thus compromising the integrity of the bus duct.
When bus bars are supported by an insulating member, whether it be a device which slides onto the conductor or one which functions as a standoff for the conductor, a dielectric material is needed between the bus bars and the insulators to fill the voids in the high potential field created therebetween. Currently, RTV silicone (room temperature vulcanizing silicone) is applied between the insulator and the bus bar to fill such voids. This is a messy and time consuming task which often leads to quality problems and added expense. Moreover, with through-type insulators, the bus bar must be centered in the slot while the RTV silicone is applied. This process can require up to 15 minutes assembly time and several days curing time for each insulator. It would be desirable to alleviate the problems associated with applying RTV silicone to save on labor expense and ultimately total system installation expense, while at the same time providing a higher quality, more efficient and less expensive bus support system.
It is also desirable to provide a ducted support chamber which is waterproofed, by eliminating outer openings in the bus duct walls. Currently, bus conductor support means are connected to bus ducts by drilling holes in the duct and bolting the support structures to the duct. This breaches the outer wall of the bus duct, thus diminishing the ability of the duct to exclude outside elements. Since power distribution networks are often located outdoors or in a contaminated environment, the integrity of the duct wall is crucial Condensation and airborne contaminants within a bus duct carrying high currents increases the likelihood that bus bars will arc between each other or arc to the bus duct itself.
Currently, heaters are often installed within ducts to remove condensation. While heaters can solve some problems with condensation., it is a rather expensive approach; thus, it would be desirable to reduce or eliminate the amount of heating required in a bus duct by improving the integrity of the bus duct.
The elimination of openings improves integrity of a duct, but this is often done at the expense of flexibility, thus making it more difficult to adjust or upgrade a power distribution system. Though such trade-offs are often necessary, it would be desirable to have a system which preserves the integrity of the bus duct and provides the flexibility of a "one size fits all" solution.